1. Field of the Invention
The present invention relates to a vehicle headlamp that has a discharge bulb and more particularly to an attachment structure of a lighting circuit unit to a lamp body of a vehicle headlamp.
2. Related Art
Discharge bulbs are capable of high luminosity irradiation, and such bulbs have been recently adopted as a light source for a vehicle headlamp. In such a vehicle headlamp, a lighting circuit unit for applying high voltage to the discharge bulb for lighting it is needed.
For a vehicle headlamp that was known when discharge bulbs began to be adopted, the lighting circuit unit was attached to a rear wall of the lamp body. However, as seen from FIG. 4, in the structure generally taken, a lighting circuit unit 130 is attached to the bottom wall 112c of a lamp body 112 where it is easy to secure an attachment space for the lighting circuit unit 130.
However, this conventional vehicle headlamp has problems. When the lighting circuit unit 130 is attached to the bottom wall 112c, most of the heat generated in the lighting circuit unit 130 following the lighting of the discharge bulb 118 is diffused upward. This promotes a temperature rise in a lamp chamber 140 heated by the lighted discharge bulb 118.
Moreover, a typical reflector 116 as shown in FIG. 4 has a lower end thereof formed with a bottom wall 116c. When the lighting circuit unit 130 is attached to the bottom wall 112c of the lamp body 112, it is necessary to secure a clearance between the bottom wall 112c and the bottom wall 116c of the reflector 116 for installing wires for a bulb socket 124 and an electric supply cord 126 that connects the lighting circuit unit 130 to the discharge bulb 118. As a result, a size reduction in the reflector 116 is inevitable to some extent, resulting in the sacrifice of corresponding light distribution performance of the lamp.
Accordingly, it is an object of the present invention to provide a vehicle headlamp in which a lighting circuit unit for the discharge bulb is attached to the lamp body so as not to cause a temperature rise in the lamp chamber and not to sacrifice light distribution performance of the lamp.
In other words, the present invention accomplishes the above objects by way applying an innovation in an attachment position of the lighting circuit unit on a lamp body.
More specifically, the above object is accomplished by a unique structure of the present invention for a vehicle headlamp that comprises a discharge bulb, a reflector for supporting the discharge bulb, a lamp body that houses the reflector therein, a transparent cover attached to a front end open portion of the lamp body, and a lighting circuit unit for lighting the discharge bulb, and in the present invention the lighting circuit unit is attached to an exterior surface of a side wall of the lamp body that is located on an inner side in the vehicle width direction.
The specific shape and attachment posture of the xe2x80x9clighting circuit unitxe2x80x9d with respect to the lamp body is not limited as long as such unit is attached to the exterior surface of the lamp body""s side wall that is located on the inner side in the vehicle width direction.
As seen from the above, the vehicle headlamp according to the present invention includes a discharge bulb, and the lighting circuit unit for lighting this discharge bulb is attached to the exterior surface of the lamp body""s side wall that is located on the inner side of the lamp body in the vehicle width direction. Accordingly, the following operational advantages are obtained.
By way of attaching the lighting circuit unit to the side wall of the lamp body, heat generated in the lighting circuit unit after the lighting of the discharge bulb is diffused upward or sideward with respect to the lighting circuit unit. Accordingly, a temperature rise in the lamp chamber can be effectively restrained.
Further, the side wall extending from the side edge of the reflector is generally not formed so that its reflecting surface is cut large from the position relatively close to the rear apex portion of the reflector as in the bottom wall. Rather, the side wall of a reflector is formed so that its reflecting surface is cut small from a position at a considerable distance in front of the rear apex portion of the reflector. Therefore, by way of attaching the lighting circuit unit to the lamp body inner side wall (and not to the outer side wall) as in the present invention, it is possible td install the electric supply cord, that extends from the lighting circuit unit, so as to be disposed along the reflecting surface back side portion of the reflector. The aiming mechanism for tilting the reflector is generally provided between the reflecting surface back portion and the side and rear walls of the lamp body; accordingly, a relatively large clearance is secured from the beginning. Therefore, contrary to the conventional structure in which the lighting circuit unit is attached to the bottom wall of the lamp body, it is not necessary in the present invention to secure a large clearance for the electric supply between the lamp body and the reflector. Thus, the size of the reflector does not need to be reduced for installing the electric supply cord.
Meanwhile, a transparent cover of a vehicle headlamp is generally inclined toward outside in the vehicle width direction and backward with respect to the vehicle headlamp. As a result, the front-end open portion of the lamp body is also inclined toward outside in the vehicle width direction and backward with respect to the lamp body. Therefore, as to the side walls of the lamp body, the side wall that is located on the inner side in the vehicle width direction has a larger area compared to the side wall that is located on the outer side in the vehicle width direction. In this regard, since the lighting circuit unit is attached to the exterior surface of the side wall on the inner side in the vehicle width direction in the present invention, a relatively large attachment space is secured.
As seen from the above, in the vehicle headlamp equipped with a discharge bulb according to the present invention, the lighting circuit unit is attached to the lamp body without causing a temperature rise in the lamp chamber or without sacrificing light distribution performance of the lamp.
In the above described structure of the vehicle headlamp of the present invention, the reflector can be designed so that a first reflector portion thereof for supporting the discharge bulb and a second reflector portion thereof for supporting a light source bulb other than the discharge bulb are disposed vertically on two levels. Accordingly, a large height dimension can be secured for the side wall of the lamp body, and therefore, the attachment space for the lighting circuit unit is further enlarged. Furthermore, in this two level design of the reflector, it is possible to dispose the electric supply cord, that extends from the light circuit unit, along the recessed area that is between the reflecting surface back side portion of the first reflector portion and the reflecting surface back side portion of the second reflector portion. Thus the space in the lamp chamber can be effectively used, thus being able to reduce the overall size of the lamp.
Moreover, in the above-described structure, the front end open portion of the lamp body is formed wrapping widely around toward outside in the vehicle width direction and backward with respect to the lamp body. In other words, the side wall of the lamp body on the outer side in the vehicle width direction does not virtually exist or is very narrow. Further, the bottom wall of such a lamp body has a wedge-like shape. Therefore, the structure of the present invention in which the lighting circuit unit is attached to the side wall on the inner side in the vehicle width direction is particularly effective. The above phrase xe2x80x9cwrapping widely around toward outside in the vehicle width direction and backwardxe2x80x9d specifically refers to the structure in which the end of the front end open portion of the lamp body on the outer side in the vehicle width direction body is positioned further to the rear than a discharge light emitting portion of the discharge bulb.
Meanwhile, when attaching the lighting circuit unit to the exterior surface of the side wall of the lamp body, it is preferable, as seen in the present invention, to attach a unit cover for covering the lighting circuit unit to the exterior surface of the side wall in order to improve the water-proof and dust-proof functions. In this case, the unit cover is attached with screws to the side wall of the lamp body at locations near upper and lower edge portions of the unit cover. With this unit cover, the strength around the attachment portion of the lighting circuit unit on the side wall of the lamp body is enhanced.
Moreover, with the above covering structure, the sealing surface of the unit cover and the side wall of the lamp body extend on a vertical plane or on a substantially vertical plane. Therefore, when water enters the unit cover, the water is easily drained out of the unit cover by its own weight. Thus, in the present invention, the unit cover has a simple waterproof structure.